Serious mental illnesses can cut life expectancy by 10 to 20 years, research has found.

smoking campaigns, the researchers from Oxford University in the UK argue in a press release.

The study looked at reviews over 20 review papers, which involved more than 1.7 million individuals and over 250,000 deaths. These review papers reported on mortality risk for a range of disorders, including mental health problems, substance and alcohol abuse, dementia, autistic spectrum disorders and childhood behavioural disorders. They also took into account studies and reviews reporting life expectancy and risk of dying by suicide.

They found that the average reduction in life expectancy in people with bipolar disorder is nine to 20 years. That reduction is similar for people with schizophrenia and depression, but increases to between nine and 24 years for people who abuse drugs and alcohol.

Heavy smokers have their life expectancy reduced by between eight to 10 years.

The findings were published in the journal World Psychiatry.

In the press release, Dr Seena Fazel of the Department of Psychiatry at Oxford University explained: “We found that many mental health diagnoses are associated with a drop in life expectancy as great as that associated with smoking 20 or more cigarettes a day.”

There are many possible reasons behind the discovery – including suicide and those with mental health problems being stigmatised and less likely to receive sufficient medical treatment.

Fazel argues that it’s important for people not to separate mental and physical illness.

“Many causes of mental health problems also have physical consequences, and mental illness worsens the prognosis of a range of physical illnesses, especially heart disease, diabetes and cancer,” he adds.